1. Field of the Invention
The present invention relates to an anion binder for a solid alkaline fuel cell, a method of preparing the same, and a membrane-electrode assembly, and more particularly, to a method of preparing an anion binder for a solid alkaline fuel cell, which is prepared in the form of nanosized powder after crosslinking, and exhibits enhanced durability to electrochemical reactions and makes it easy to fabricate electrodes.
2. Discussion of the Related Art
A fuel cell is a device that generates electrical energy from fuel and air supplied from the outside by using electrodes. The fuel cell has the advantage of improving the efficiency of fuel use and generating less environmental pollutants such as emissions. Moreover, while the existing primary and secondary cells are devices that charge and discharge a limited amount of energy, fuel cells produce electrical energy continually for as long as fuel is supplied. Hence, there is much research conducted on the fuel cells, which are emerging as the next generation clean energy source.
An ion-exchange membrane is a kind of polymer separation membrane, which is capable of selectively separating anions and cations depending on the type of ion exchange group introduced into the membrane. For a cation exchange membrane, which is available for commercial use, the ion exchange groups are roughly classified into strongly acidic sulfonic acid groups (—SO3—) and weakly acidic carboxylic acid groups (—COO—). For an anion exchange membrane, a strong basic quaternary ammonium group (—N+R3) is usually used as the ion exchanger.
Such ion exchange membranes are used in electrolysis for desalination and purification, water-splitting electrolysis, diffusion dialysis for recovery of acid from an acid waste solution, electrodeionization for ultrapure water production, and so on. Moreover, following the recent report about the possibility of using an anion-exchange membrane for fuel cells, more and more research is being conducted to use an anion-exchange membrane for fuel cells.
A fuel cell includes a fuel electrode (anode) for supplying hydrogen ions and electrons from hydrogen or methanol and an air electrode (cathode) for supplying oxygen. A fuel cell produces electricity on the principle that when fuel is supplied from the fuel electrode, the fuel is divided into hydrogen ions and electrons, the hydrogen ions are combined with oxygen supplied from the air electrode through an electrolyte membrane to form water, and the electrons separated from the fuel in the fuel electrode produce current through an external circuit, thereby generating electricity, heat, and water by an electrochemical reaction, which is the reverse of electrolysis of water. Different types of fuel cells include polymer electrolyte membrane fuel cells (PEMFC), direct methanol fuel cells (DMFC), direct borohydride fuel cells (DBFC), and solid alkaline fuel cells (SAFC). Among these types of fuel cells, the polymer electrolyte membrane fuel cells, the direct methanol fuel cells, and the direct borohydride fuel cells have to employ a cation-exchange membrane, a cation or hydrogen-ion conducting electrolyte membrane, as the electrolyte. On the other hand, the solid alkaline fuel cells and the direct borohydride fuel cells have to employ an anion-exchange membrane, a hydroxyl-ion conducting electrolyte membrane, as the electrolyte. The direct borohydride fuel cells can use both the cation-exchange membrane and the anion-exchange membrane.
Unlike fuel cells employing a cation-exchange membrane, fuel cells employing an anion-exchange membrane can use non-precious metal catalysts or non-platinum catalysts for electrodes, thus achieving cost reduction. Accordingly, research on the preparation of anion-exchange membranes is increasingly conducted for the development of fuel cells employing an anion-exchange membrane.
Meanwhile, non-crosslinked polymer has been conventionally used as a binder used for a membrane-electrode assembly of a solid alkaline fuel cell. The non-crosslinked polymer was problematic in terms of durability because it is easily deteriorated by an electrochemical reaction. There have been attempts to use a crosslinked binder in order to solve this problem. Korean Patent Registration No. 0738058 discloses a fuel cell electrode including: a support; and a catalyst layer formed on the support, the catalyst layer including: a support catalyst; and a polymerization product obtained by the polymerization of a mixture of a polyurethane compound and polyethylene(meta) acrylic acid, a method of preparing the same, and a fuel cell having the same. However, such a crosslinked binder causes problems in the production of electrode slurry resulting from the crosslinking of polymer resin.
As such, the present inventors perfected the present invention after conducting research on ways to improve durability to electrochemical reactions and solve the problems occurring in the production of electrode slurry.